Electric fusible elements of the type commonly used in conjunction with electric cutouts normally include a strain wire together with a fusible element which are connected in parallel and which function in known manner. In order to utilize an electric cutout as a load break device, a tensile force is applied to the fuse link and mechanically ruptures both the strain wire and the fusible element thereby to initiate circuit interruption.
In some instances the fuse link of an electric cutout includes a straight strain wire normally maintained in tension together with a helical fusible element which is in parallel circuit relation with the strain wire. In such constructions a mechanical tensile force applied to the strain wire and to the fusible element effectively breaks the strain wire but may not have sufficient travel in order to rupture the helical fusible element which may simply extend in length as a coiled spring but without being broken.
In instances in which a helical fusible element is used, it is necessary to impart a substantial tensile force initially thus to break the strain wire and thereafter to impart a substantial distance of travel to the end of the helical element by the force applying mechanism which travels over a substantial distance thereby to stretch and then to break the helical element.
U.S. Pat. No. 2,836,681 issued May 27, 1958 discloses a link break cutout wherein the thrust of a linkage mechanism imparts an initial force of substantial magnitude and thereafter due to the change in angular relationship of the linkage mechanism to the force applying structure effects a substantial reduction in force applied and which increases the degree of travel of the link breaking mechanism.
U.S. Pat. No. 2,835,764 issued May 20, 1958 is said to constitute an improvement over U.S. Pat. No. 2,836,681 and utilizes an arrangement wherein the first part of opening movement toward breaking fusible elements utilizes a cam which rides on a pivoted part to impart substantial fuse link breaking force. Thereafter a gear segment on a manually movable part engages a pinion to impart rotary motion to the pinion together with a certain travel distance to the separated portions of the strain wire and to the fusible element.